Field of the Invention
The present invention relates to a drive shaft and a manufacturing method therefor, in which the drive shaft is connected to and transmits torque between constant velocity joints.
Description of the Related Art
In automobiles that are driven electrically or by an engine, power (rotational torque) is transmitted to the drive wheels from the engine or a motor through a power transmission device disposed between the drive wheels and a reduction gear. The power transmission device, in general, is equipped with constant velocity joints (constant velocity universal joints) arranged at an interval at two locations in an axial direction, and a drive shaft connected to the constant velocity joints and which transmits torque therebetween. More specifically, in order to suitably transmit the aforementioned torque, the drive shaft must be constituted from a material that is superior in torsional strength as well as fatigue strength. As the material for such a drive shaft, carbon steel, the hardness of which is increased by induction hardening, has generally been used.
Incidentally, in recent years, attempts have been made to lessen the weight of an automobile with the aim of reducing fuel consumption or the like. From this standpoint, in order to reduce the weight of the drive shaft within a range in which sufficient torsional strength and fatigue strength can be maintained, a reduction in diameter or a so-called thin-walled portion may be provided on the drive shaft. However, there is a limit to which weight can be reduced by such a technique.
Thus, in order to effectively reduce the weight of the drive shaft, for example, as the material of the drive shaft, there can be used a carbon fiber composite material (carbon fiber reinforced plastic, CFRP) which is lighter in weight than carbon steel. In this case, it is necessary that both ends of the drive shaft are formed in shapes that enable constant velocity joints to be attached thereon, and there is a concern that, if CFRP is used, sufficient machining precision cannot be obtained. On the other hand, the central part of the drive shaft has few restrictions on the shape thereof, as was described above. Consequently, opposite ends of the drive shaft are constituted from a metallic member such as carbon steel, whereas preferably the central part is composed of a CFRP member. In order to obtain such a drive shaft, it is necessary that the metallic member and the CFRP member be joined together.
As a method for firmly joining the metallic member and the CFRP member, a mechanical joining technique such as riveting or the like is generally known. Further, for example, as disclosed in Japanese Laid-Open Patent Publication No. 05-215119, in order to manufacture a propeller shaft, a method is proposed for joining the ends of a cylindrical metallic member and a CFRP member by an adhesive.